1. Field of the Invention
The present disclosure relates to technology for a medical implant and specially a local degradable porous intervertebral implant which is made from degradable hydroxyl apatite and metal block and steadily merged in upper and lower bones during osteoconduction and bone regeneration.
2. Description of the Prior Art
The intervertebral fusion surgery is known for “spinal fusion” linking two opposing vertebrae from which an intervertebral disc has been removed. In general, the intervertebral fusion surgery is used to treat spinal lesions such as spinal degeneration and slipped disc, each of which causes persistent backache, sciatica or leg weakness. The intervertebral fusion surgery is also an important part of a spinal deformation surgery for scoliosis, spondylolisthesis, and spine trauma.
As one substance to repair osseous tissues, an implant which features biological absorption in addition to its supporting capability will be ideal in practice. An existing spinal fusion device disclosed in U.S. Pat. No. 5,645,598 consists of a metal framework and bio-absorbable materials therein. Embedded between two opposing vertebrae for recovery of osseous tissues, the implant which has insufficient hardness and volume less than vertebrae themselves may sink and damage osseous tissues between opposing vertebrae wearing each other, particularly end planes of vertebrae.
Moreover, most existing supports made from biodegradable polymers for tissue engineering technology belong to a porous structure infiltrated by living cells usually taken from a patient's body during cell culture. Some time after, the support in which cells grow will be implanted in an animal losing immunocompetence (e.g., rat) or a patient (e.g., patient's subcutaneous tissues for subsequent operation). In the next few weeks or months, the cells relying on nutrients supplied by the animal or the patient propagate quickly but the support are dissolved and absorbed. Finally, the implant (real osseous tissues) can be removed from the animal or the patient's subcutaneous tissues and further planted in an injured area to be treated. The above descriptions are presented in U.S. Pat. Nos. 6,139,578, 6,200,606, 5,306,303 and 6,132,463.
A bio-absorbable support with abundant pores inside for tissue engineering technology will be a fine material. For example, porous calcium phosphate cement with pore-forming agents as shown in Patent No. CN 119346A are made of ordinary calcium phosphate cement and pore-forming agents containing sparingly soluble salt, acid salt, basic salt or surfactant or a mixture thereof. However, the calcium phosphate cement classified as bone cement without fixed form is characteristic of poor mechanical strength and incompetent for bone fusion independently.
Another example is a technology method for producing porous magnesium/hydroxyl apatite as shown in Patent No. CN 101099873A. The method is intended to create porous hydroxyl apatite with hydroxyl apatite powders and magnesium powders mixed proportionally and experiencing cold press molding and sintering for vaporizing magnesium. However, the problem of poor mechanical strength still exists in porous hydroxyl apatite with magnesium removed at high temperatures.
A further example is porous degradable magnesium alloy bone scaffold material containing HA (hydroxyl apatite) nano powders as shown in Patent No. CN 101797400A. The porous degradable magnesium alloy bone scaffold material is made from magnesium powders with a trace of refined zinc crystalline grains (magnesium-zinc alloy, 50 to 80%), HA nano powders (10 to 20%) and pore-forming agents (10 to 30%). However, the problem of poor mechanical strength still exists in porous hydroxyl apatite with magnesium removed at high temperatures.
Furthermore, the conventional porous hydroxyl apatite (HA) materials sintered at high temperatures (>1000° C.) feature insufficient micro-sized or nano-sized pores and are difficultly absorbed by a living body. In the other hand, the disadvantages of conventional biodegradable polymers for bone scaffolds are weak mechanical strength and fast dissolution rate. It can be seen from above descriptions that a porous metal material for medical purposes which facilitates osteoconduction, light weight and biological combination should be developed.
Having considered drawbacks derived from conventional porous metal materials for osteoconduction, the inventor studied continuously to develop an intervertebral implant in the present disclosure.